Substituted (4-benzimidazol-2-ylmethylamino)-benzamidines, particularly dabigatran etexilate (CAS 593282-20-3), are already known from International Patent Application WO 98/37075 as active substances with a thrombin-inhibiting and thrombin time-prolonging activity. The main indication sectors of the compound of chemical formula I are the postoperative prophylaxis of deep vein thromboses and stroke prevention (prevention of stroke due to atrial fibrillation, SPAF for short).
In WO 98/37075 it is proposed to produce the substituted (4-benzimidazol-2-ylmethyl-amino)-benzamidines by reacting corresponding substituted (4-benzimidazol-2-ylmethylamino)-benzonitriles with ammonia. This process is extremely onerous from the manufacturing point of view and results in a large quantity of acids that have to be disposed of (cf. also WO 2007/071743, WO 2007/071742).
An improved process for preparing dabigatran etexilate and analogous compounds thereof is described hereinafter. By switching to new starting materials, the use of phase transfer catalysis and the formation of the benzimidazole without the use of coupling reagents a significantly more efficient synthesis of dabigatran etexilate is achieved. The high selectivity in the coupling of the intermediates (step 2) contributes significantly to the economy of the new synthesis route.